Methyl (2 E )-3-[3-Benzyl-2-(3-methoxy-3-oxoprop-1-yn-1-yl)-2-(1-naphthyl)imidazolidin-1-yl]acrylate

: Compounds with propargylamine moiety are useful synthetic precursors of several important classes of nitrogen-containing heterocycles. The title compound, methyl (2 E )-3-[3-benzyl- 2-(3-methoxy-3-oxoprop-1-yn-1-yl)-2-(1-naphthyl)imidazolidine-1-yl]acrylate, has been prepared by domino-reaction, employing easily available 1-benzyl-2-(1-naphthyl)-4,5-dihydro-1 H -imidazole and methyl propiolate in a high 92% yield. The structure of title compound was determined using 1 H-NMR, 13 C-NMR, UV, FT-IR and HRMS (High-Resolution Mass Spectrometry).


Introduction
Propargylamines are widely used as convenient synthetic intermediates for the preparation of various heterocyclic and pharmaceutically relevant compounds [1][2][3].A special place among propargylamines is occupied by N-vinylpropargylamines due to the fact that the profile of their reactivity includes [3,3]-sigmatropic aza-Claisen rearrangement as well as 5-exo-dig-and 6-endo-dig-cyclizations, leading to such attractive heterocyclic compounds as pyrroles and pyridines [4][5][6][7][8][9][10][11][12][13][14].Recently, we have proposed a new type of N-vinylpropargylamines, which can be easily obtained by the reaction of 1,2-disubstituted 2-imidazolines with such electron-deficient alkynes as methyl propiolate or acetylacetylene [15].It was also shown that refluxing these compounds in o-xylene solution under aerobic conditions led to polysubstituted pyrroles through a domino-sequence starting with [3,3]-sigmatropic aza-Claisen rearrangement and final oxidative step.At the same time, the synthetic potential of such propargylamines, in our opinion, is far from being exhausted.Herein, we report a convenient preparative synthesis of a new derivative from the aforementioned group of compounds, containing a condensed aromatic fragment as a substituent.
The structure determination of the title compound 4 was performed with 1 H-and 13 C-NMR spectroscopy, IR and UV spectroscopy, and also mass spectrometry.In the 1 H-NMR spectrum, six protons of the two methoxy groups of ester fragments of propiolic and aminoacrylic acids appeared as two peaks at 3.51 ppm (s, 3H) and 3.89 ppm (s, 3H).Two protons of the methylene group of the benzyl fragment appeared in the spectrum as two doublets at 3.56 ppm (1H) and 4.68 ppm (1H), which confirms the presence of chiral carbon atom in the product structure.CH-protons of the double bond of the aminoacrylic acid residue, containing an electron-withdrawing ester group on the one hand and an electron-donating nitrogen atom of the imidazolidine fragment on the other, appeared as two doublets at 4.68 ppm and 7.11 ppm with constant 13.1 Hz which is characteristic for CH-protons of double bond in trans-configuration.In the IR spectra of adduct 4, there is a band at 2220 cm −1 , characteristic for stretching vibrations of the triple bond; a high-intensity band at 1715 cm −1 , characteristic of vibrations of the carbonyl groups of ester fragments; and at 1614 cm −1 , characteristic for stretching vibrations of the double bond.The brutto formula was devised with the help of high-resolution mass spectrometry.The spectral characteristics of α-naphthyl derivative 4 were in good agreement with the data of previously obtained analogous compounds.
In summary, using the elaborated method, compound 4 has been synthesized for the first time in a high yield.These results can be useful for further research on propargylamines and their subsequent transformations.

General
Starting reagents were purchased from commercial sources and were used without any additional purification (Acros Organics, Geel, Belgium). 1 H and 13 C-NMR spectra were acquired on a Jeol JNM-ECA 600 spectrometer (Jeol Ltd, Tokyo, Japan) (with operating frequencies of 600 and 150 MHz, respectively) at room temperature and referenced to the residual signals of the solvent.The solvent used for NMR was CDCl3.Chemical shifts are reported in parts per million (δ/ppm).Coupling constants are reported in Hertz (J/Hz).The peak patterns are indicated as follows: s, singlet; d, doublet; t, triplet; q, quadruplet; m, multiplet; dd, doublet of doublets and br s, broad singlet.Infrared spectra were The mechanism of imidazolidine 4 formation includes the conjugated addition of 2-imidazoline (1) at the triple bond of the first alkyne molecule, leading to the zwitterion (3), which then deprotonates the second methylpropiolate molecule to form an acetylenide ion.At the final stage, nucleophilic addition of the obtained acetylenide ion occurs at the position 2 of the 2-imidazolinium ion.Thus, this interaction is an example of a pseudo three-component domino reaction.
The structure determination of the title compound 4 was performed with 1 H-and 13 C-NMR spectroscopy, IR and UV spectroscopy, and also mass spectrometry.In the 1 H-NMR spectrum, six protons of the two methoxy groups of ester fragments of propiolic and aminoacrylic acids appeared as two peaks at 3.51 ppm (s, 3H) and 3.89 ppm (s, 3H).Two protons of the methylene group of the benzyl fragment appeared in the spectrum as two doublets at 3.56 ppm (1H) and 4.68 ppm (1H), which confirms the presence of chiral carbon atom in the product structure.CH-protons of the double bond of the aminoacrylic acid residue, containing an electron-withdrawing ester group on the one hand and an electron-donating nitrogen atom of the imidazolidine fragment on the other, appeared as two doublets at 4.68 ppm and 7.11 ppm with constant 13.1 Hz which is characteristic for CH-protons of double bond in trans-configuration.In the IR spectra of adduct 4, there is a band at 2220 cm −1 , characteristic for stretching vibrations of the triple bond; a highintensity band at 1715 cm −1 , characteristic of vibrations of the carbonyl groups of ester fragments; and at 1614 cm −1 , characteristic for stretching vibrations of the double bond.The brutto formula was devised with the help of high-resolution mass spectrometry.The spectral characteristics of α-naphthyl derivative 4 were in good agreement with the data of previously obtained analogous compounds.
In summary, using the elaborated method, compound 4 has been synthesized for the first time in a high yield.These results can be useful for further research on propargylamines and their subsequent transformations.

General
Starting reagents were purchased from commercial sources and were used without any additional purification (Acros Organics, Geel, Belgium). 1 H and 13 C-NMR spectra were acquired on a Jeol JNM-ECA 600 spectrometer (Jeol Ltd, Tokyo, Japan) (with operating frequencies of 600 and 150 MHz, respectively) at room temperature and referenced to the residual signals of the solvent.The solvent used for NMR was CDCl 3 .Chemical shifts are reported in parts per million (δ/ppm).Coupling constants are reported in Hertz (J/Hz).The peak patterns are indicated as follows: s, singlet; d, doublet; t, triplet; q, quadruplet; m, multiplet; dd, doublet of doublets and br s, broad singlet.Infrared spectra were measured on an Infralum FT-801 FT/IR instrument (Simex, Novosibirsk, Russia).The wavelengths are reported in reciprocal centimeters (νmax/cm −1 ).UV spectra were recorded using Varian Cary 50 (Agilent, Santa Clara, CA, USA).Mass spectra were recorded with LCMS-8040 Triple quadrupole liquid chromatograph mass-spectrometer from Shimadzu (ESI) and Kratos MS-30 mass-spectrometer (EI, 70 eV) (Shimadzu, Tokyo, Japan).HRMS spectra were recorded on a Bruker MicrOTOF-Q II (Bruker, Billerica, MA, USA).The reaction progress was monitored by TLC and the spots were visualized under UV light (254 or 365 nm) (UVGL-25, UVP, Upland, CA, USA).Column chromatography was performed using silica gel (60-75 mesh) (Merck KGaA, Darmstadt, Germany).Melting points were determined on a SMP-10 apparatus (Stuart, Stone, UK) and were uncorrected.Solvents were distilled and dried according to standard procedures.

Supplementary Materials:
Copies of 1 H-, 13 C-NMR, IR, UV and HRMS spectra are available online.

Scheme 1 .
Scheme 1. Preparation of the title compound.

Scheme 1 .
Scheme 1. Preparation of the title compound.

Author Contributions:
Conceptualization, N.E.G. and L.G.V.; methodology, N.E.G. and A.S.G.; investigation, A.S.G.; writing-original draft preparation, N.E.G.; writing-review and editing, A.S.G. and L.G.V.; funding acquisition, N.E.G.All authors have read and agreed to the published version of the manuscript.